The invention relates to a method for determining a straight line intersecting the axis of an optical radiation beam of a photoelectric levelling apparatus, where the optical radiation beam transmits power from a stable radiation transmitter to a stable radiation receiver and by screening the optical radiation beam and by evaluation of the signal detected by the radiation receiver. The invention relates furthermore to an arrangement for execution of this method.
One of known arrangements for photoelectric levelling is based on a method of the measuring the distance from a straight reference line inside the optical radiation beam, the line being determined by screening this beam by screening means to a constant value of the signal detected by the radiation receiver.
Another known arrangement for photoelectric levelling is based on the method of a simultaneous screening of two parallel optical radiation beams by a single common screen. By this method an optical straight reference line is determined, which is the axis of symmetry of both optical radiation beams, by screening both beams to the same depth by a common screen.
A drawback of both said methods and arrangements is primarily that the accuracy of determination of the optical straight reference line depends on the stability of the intensity of the transmitted optical radiation beam, so that in case of a variation of this intensity also the values corresponding to a certain position of the screening screen are varying, reducing the accuracy of the whole arrangement for photoelectric levelling. A drawback of the second mentioned method and arrangement for photoelectric levelling is the necessity of application of two optical radiation beams and the necessity of an independent detection of both these optical radiation beams, where for instance collimated laser radiation beams have to be used for spatial separation of the optical radiation beams.